Process for producing titanium dioxide pigment for photograph and photographic support comprising same

ABSTRACT

Disclosed is a process for producing a titanium dioxide pigment used for a resin-coated paper type photographic support, comprising the following steps: 
     (a) a step of adding at least one alkaline earth metal compound in an amount of 0.01-2.0% by weight in terms of a metal oxide based on the titanium dioxide before calcination step and 
     (b) an acid-washing step of washing the titanium dioxide at acidic state after the calcination step and before a step of surface treatment with a hydrated metal oxide, 
     and wherein particle size of the titanium dioxide pigment is 0.110-0.150 μm shown by number-average diameter obtained by measuring the diameter in a certain direction using an electron microscope. A photographic support which comprises the above titanium dioxide pigment is also disclosed. Occurrence of die lip stain and microgrit are substantially reduced in the photographic support and a photographic material made thereof exhibits improved image sharpness.

This is a continuation of application Ser. No. 08/094,951, filed on Jul.22, 1993, which was abandoned upon the filing hereof which is aDivisional of Ser. No. 07/714,847, filed Jun. 13, 1991, now U.S. Pat.No. 5,264,033.

BACKGROUND OF THE INVENTION

The present invention relates to a process for producing a titaniumdioxide pigment useful for photograph and a photographic supportcomprising it. More particularly, it relates to a photographic supportin production of which occurrence of die lip stain and microgrit issubstantially retained, and which meets requirements of a highersharpness.

Since resin-coated paper type photographic supports were developedseveral ten years ago, various patent applications have been madethereon and considerable improvements have been made in their qualityand in production technique thereof.

It is not too much to say that all of the problems relatively easy toimprove have been solved until now.

At present, important problems which have not yet been fully improved inspite of the efforts made by the manufacturers in this field areso-called die lip stain and microgrit in production thereof.

Patent applications on solution of the problem of die lip stain (die lipstreaks) were filed in comparatively earlier time. For example, a methodin which zinc oxide and a specific dispersant are contained in acomposition of a resin and a titanium dioxide pigment is proposed inJapanese Patent Application Kokai No. 53-02947. For improvement inrespect of resin, Japanese Patent Application Kokai No. 57-109948discloses to limit a specific characteristic value n and for improvementin respect of a titanium dioxide pigment, Japanese Patent ApplicationKokai No. 58-17433 discloses to use titanium dioxide pigments in whichthe surface of particles is coated with di- tetra-hydric alcohols.

However, solution of the problem of die lip stain is so difficult thatsatisfactory photographic support has not yet been obtained by onlyimproving materials and use of materials in combination.

The microgrit which originates from resin per se has been the problemcalled resin gel in the field of resins for a long time. Furthermore, inthe case of masterbatch containing a titanium dioxide pigment, it hasbeen known as microgrit. This problem is described, for example, inJapanese Patent Application Kokai No. 59-1544, pages 3-4.

Although not concerning with a process for producing a titanium dioxidepigment for photograph, Japanese Patent Application Kokoku No. 50-36440discloses a process for producing a pigment titanium dioxide, whichcomprises the steps of

(a) hydrolyzing a solution of titanium sulfate to produce a precipitateof hydrated titanium dioxide,

(b) washing the precipitate,

(c) treating the thus washed precipitate with at least one treatingagent selected from lithium, beryllium, aluminum, magnesium, zinc,sodium, potassium, rubidium, cesium, and compounds of these metals,

(d) treating the precipitate with a volatile ammonium compound, and

(e) introducing the precipitates obtained in the steps (c) and (d) intofutile forming seed and calcining it at 750°-1000° C.,

wherein pH of the above wet precipitate is 6-10 just before thecalcination and the precipitate just before the calcination isaccompanied by

(i) at least 0.7% by weight in total of volatile ammonium compound (oneor more kinds) (in terms of ammonium sulfate based on the weight oftitanium dioxide),

(ii) totally 0.02-0.50% by weight of a treating agent selected fromberyllium, aluminum, magnesium, zinc, and compounds of these metals (interms of metal oxide based on the weight of titanium dioxide), and

(iii) 0.05-1.0% by weight of a treating agent selected from the groupconsisting of sodium, potassium, rubidium, cesium, and compounds ofthese alkali metals (in terms of alkali metal oxide based on the weightof titanium dioxide), with a proviso that lithium and/or at least onelithium compound may be substituted with one or all of the treatingagents selected from the group referred to in the above (ii) and/or(iii).

This patent publication discloses treatment with lithium and otherseveral kinds of metals and compounds thereof, but also discloses thatlithium and/or at least one lithium compound is partially or totallysubstituted in preference to the other metals and compounds thereof. Thepublication makes no mention of limitation to a specific particle sizeand besides, the objects thereof are improvements of lightness (Lvalue), coloring power and texture.

Furthermore, Russian Patent No. 975576 discloses a rutile type titaniumdioxide pigment prepared through an acid washing step after acalcination step as a titanium dioxide pigment which can be used formaking a photographic paper. However, this patent makes mention ofneither die lip stain nor microgrit. Further, the object thereof is toreduce photographic activity. This is referred to on pages 14-16 ofJapanese Patent Application No. H.1-58943.

Taking into consideration the above prior art, problems (tasks) to besolved by the present invention will be explained in detail.

Recently, demand for photographic supports of high quality, for example,of high sharpness has more and more increased and tendency to increasecontent of a titanium dioxide pigment in a resin layer of a photographicsupport has increased.

When concentration of a titanium dioxide pigment in a resin layer of athermoplastic resin-coated paper is raised, a photographic support onwhich a printed image high in sharpness can be obtained, but seriousproblems often occur in photographic properties and productiontechnique. That is, when a thermoplastic resin composition, especially apolyolefin resin composition, which contains a titanium dioxide pigmentis melt extruded into a film from a slit die and applied to a substrate,a sticking matter or a stain in the form of a needle or an icile(hereinafter referred to as "die lip stain") tends to be formed on thetip of die lip after a short run extrusion. Since the die lip staintends to grow larger with lapse of time of the run, it is verytroublesome.

If this die lip stain occurs during melt extrusion coating, streaks aregenerated on the surface of the thus produced thermoplastic resin-coatedpaper or the stain sometimes comes off and sticks to the resin layer,resulting in a foreign matter. Therefore, the surface property of thethermoplastic resin-coated paper is seriously damaged, and such paper isutterly unsuitable as a photographic support which requires excellentsurface property and has no commercial value. In order to removecompletely the die lip stain once formed, the production has to be shutdown to clean the die lip or exchange the die. The cleaning orexchanging requires much labor and time, resulting in considerablereduction of productivity.

A further problem is that in a photographic support coated with athermoplastic resin composition, especially a polyolefin resincomposition, which contains a titanium dioxide pigment, fine foreignmatters or particles called microgrit are apt to be formed on thesurface of the resin containing the titanium dioxide pigment on theimage forming side of the support.

If microgrit is formed on a resin-coated paper used as a photographicsupport, serious photographic problems are brought about. That is, whena portrait is developed on a photographic paper using a photographicsupport of a resin-coated paper having microgrit, and if the microgritappears in the portion of a face or the like, commercial value of thepaper is completely lost. This microgrit also tends to be generated moreoften when concentration of a titanium dioxide pigment in the resinlayer of the thermoplastic resin-coated paper is increased.

SUMMARY OF THE INVENTION

As mentioned above, for obtaining a photographic support which canprovide a printed image of high sharpness in an attempt to meet thedemand of customers, concentration of a titanium dioxide pigment in aresin layer of the thermoplastic resin-coated paper must be as high aspossible and die lip stain and microgrit are more conspicuouslygenerated.

The present invention has been accomplished for solving these seriousproblems.

That is, the present inventors have functionally investigated theproduction steps from preparation of a titanium dioxide pigment toproduction of a photographic support and as a result, they have found amethod for producing a titanium dioxide pigment for photograph which isvery suitable for use in a photographic support, and which causes leastformation of die lip stain and microgrit even if sharpness of a printedimage to be formed thereon is increased. Thus, the present invention hasbeen accomplished.

The present invention provides a method for producing a titanium dioxidepigment to be used in a resin-coated paper type photographic supportwhich comprises a substrate such as a paper, a synthetic paper or a filmwhich is coated with a thermoplastic resin composition containing athermoplastic resin and a titanium dioxide pigment on at least one side,wherein the titanium dioxide pigment is produced through productionsteps including the following steps:

(a) a step of adding at least one alkaline earth metal compound in anamount of 0.01-2.0% by weight in terms of a metal oxide based on thetitanium dioxide before calcination step and

(b) an acid-washing step of washing the titanium dioxide at acidic stateafter the calcination step and before a step of surface treatment with ahydrated metal oxide,

and wherein particle size of the titanium dioxide pigment is 0.110-0.150μm, shown by number-average diameter obtained by measuring the diameterin a given direction using an electron microscope.

The present invention further provides a resin-coated paper typephotographic support comprising a substrate such as a paper, a syntheticpaper or a film coated with a thermoplastic resin composition containinga thermoplastic resin and a titanium dioxide pigment on at least oneside, wherein the titanium dioxide pigment comprises the titaniumdioxide pigment produced as mentioned above.

That is, the present invention relates to a method for producing atitanium dioxide pigment very suitable for using in a photographicsupport, wherein said titanium dioxide pigment is produced throughcalcination step after addition of an alkaline earth metal compound andthrough the subsequent acid-washing step conducted at a specific stageof production steps and wherein the titanium dioxide pigment has aparticle size within a specific range and the present invention furtherrelates to a photographic support in which the above-mentioned titaniumdioxide pigment is used and die lip stain and microgrit are generatedquite a little and which can provide a high sharpness.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be explained in detail.

Representative method for producing the titanium dioxide pigment used inthe present invention is a sulfuric acid method comprising the followingsteps.

Raw titanium dioxide→digestion, extraction→allowing to stand,crystallization→filtration,concentration→hydrolyzation→washing→calcination.fwdarw.grinding,screening→wet grinding, classification→surface treatment→washing,drying→finishing grinding→titanium dioxide pigment

In the sulfuric acid method, ferric sulfate is usually crystallized froma solution of ilmenite in sulfuric acid and then removed and theresulting aqueous titanyl sulfate solution is hydrolyzed to obtainhydrated titanium oxide, which is calcined to improve the properties asa pigment. The hydrolysis of the aqueous titanyl sulfate solution can becarried out by a so-called self seed method which comprises adding theaqueous titanyl sulfate solution to warm water to precipitate hydratedtitanium oxide, which is used as a seed, or a so-called external seedmethod which comprises adding, as a seed, titanium hydroxide prepared byneutralizing titanyl sulfate or titanium tetrachloride.

The titanium dioxide pigment used in the present invention is preparedby adding an alkaline earth metal compound before the calcination step,wherein preferred steps are to wash titanium dioxide afterhydrolyzation, then to place it, after thickening on a filter or thelike, in a mixer, e.g. a kneader, to which the alkaline earth metalcompound is added and mixed well, and finally to calcine the mixture.

As the alkaline earth metal compound, there may be used sulfates,nitrates, chlorides, carbonates, hydroxides, oxides and the like ofvarious alkaline earth metals and examples thereof are berylliunhydroxide, magnesium hydroxide, magnesium sulfate, magnesium carbonate,magnesium chloride, calcium hydroxide, strontium chloride and bariumchloride. Preferred are magnesium compounds and barium compounds.

The titanium dioxide pigment used in the present invention has aparticle diameter of 0.110-0.150 μm in terms of a number-averagediameter measured in a given direction using an electron microscope. Inthe case of a photographic support coated with a thermoplastic resincomposition containing titanium dioxide pigment having a number-averagediameter of less than 0.110 μm, die lip stain tends to occur oftenduring production and occurrence of microgrit is also conspicuous andbesides, sharpness of a printed image formed on the photographic supportis low. On the other hand, a photographic support coated with athermoplastic resin composition containing titanium dioxide pigmenthaving a number-average diameter of more than 0.150 μm has the problemthat sharpness of a printed image formed thereon is appreciably low.Thus, the titanium dioxide pigment used in the present invention haspreferably a number-average diameter of 0.110-0.150 μm for reducing dielip stain and microgrit during production of photographic support, andfor maintaining high sharpness of a printed image of high sharpness. Thetitanium dioxide pigment having a number-average diameter of 0.110-0.150μm can be obtained by producing it under production conditions adjustedto optimum. Production conditions for the titanium dioxide pigment,especially calcination conditions such as calcination temperature,calcination time, and kind and amount of the alkaline earth metalcompound allowed to be present at the time of calcination can bedetermined by obtaining the number-average diameter by measuring thediameter in a given direction of the titanium dioxide pigment producedunder conditions of a series of combined experiments, the measurement ofthe diameter in a certain direction being carried out using an electronmicroscope. In this case, the typical calcination conditions forobtaining larger number-average diameter are high calcinationtemperature, long calcination time, and small amount of the alkalineearth metal compound present at the time of calcination. On the otherhand, the typical calcination conditions for obtaining smallnumber-average diameter are low calcination temperature, shortcalcination time, and large amount of the alkaline earth metal compoundto be present at the time of calcination. Especially preferredcalcination conditions for the titanium dioxide pigment used in thepresent invention are combinations of 800°-1100° C. as a calcinationtemperature, 15 minutes-5 hours as a calcination time and 0.01-2.0% byweight in terms of metal oxide based on titanium dioxide as an amount ofthe alkaline earth metal compound to be present at the time ofcalcination.

Besides, if necessary for operation, various inorganic compound asdisclosed in Japanese Patent Application Kokoku No. 48-18718 may beadded.

In the present invention, any of rutile type titanium dioxide pigment,anatase type titanium dioxide pigment, mixed crystal titanium dioxidepigment of rutile type and anatase type, and mixtures thereof can beused, but rutile type is preferred for obtaining a photographic supportwhich can provide a printed images of especially high sharpness.

The product which has been subjected to calcination step in this way ishereinafter referred to as "titanium dioxide clinker" or merely"clinker". The clinker is ground in a dry state by a centrifugal rollermill such as Raymond mill; air mill; and the like and the ground productwas suspended in water to make a titanium dioxide slurry and this slurryis further subjected to wet grinding in a wet ball mill or vibrationmill and then, is subjected to wet classification by centrifugalseparation using a continuous type horizontal centrifugal separatorand/or by passing through a vibration type double-deck screen (U.S.standard screen: 325 mesh) to obtain a titanium dioxide slurrysubstantially free from coarse particles (which is hereinafter referredto as "fines"). The fines from which coarse particles have been removedand which are still in the form of slurry are subjected to acid-washingat acidic state and thereafter, the titanium dioxide particles aresurface treated with a specific amount of a hydrated metal compound.After the surface treatment, the slurry is filtered and washed withwater using a filter press and is further finely ground by an impactgrinder and/or a fluid energy mill to obtain a titanium dioxide pigment.

In the present invention, a titanium dioxide having rutile structure(hereinafter sometimes referred to as "rutile type titanium dioxide")means one which comprises at least 90% by weight, preferably at least95% by weight of rutile structure in its crystal structure. Furthermore,the number-average diameter here means a value obtained by measuring thelength in a given direction of 1000 titanium dioxide particles andaveraging the obtained values and is shown by μm.

The titanium dioxide pigment used in the present invention is preferablyprepared by subjecting to acid-washing after the wet grinding. Theacid-washing can be carried out, for example, by a method whichcomprises adding to the titanium dioxide slurry a mineral acid such assulfuric acid, hydrochloric acid or nitric acid, preferably sulfuricacid, if necessary, diluted with water, namely, in the form of a dilutemineral acid such as a dilute sulfuric acid, washing the slurry withstored water, and removing the supernatant, a method which comprisesrepeating the above procedure several times, or a method which comprisesacid-washing the titanium dioxide slurry with flowing water on a filter.Concentration of the titanium dioxide slurry in the acid-washingtreatment is preferably 100-300 g/l and acidity of the slurry ispreferably 3 or less, more preferably 2 or less in pH value. Temperatureof the slurry in the acid-washing treatment, namely, acid-washingtemperature is preferably from room temperature to 90° C., morepreferably 40°-80° C. With reference to acid-washing time, it ispreferred to carry out the acid-washing for about 10 minutes-2 hours andrepeat it several times in the case of the method of using the storedwater and for at least 2 hours in the case of using the flowing water.

The thus acid-washed titanium dioxide slurry is subjected to a series oftreatments of surface treatment, dehydration, water-washing, drying andgrinding to obtain a titanium dioxide pigment.

The treatment of the surface of titanium dioxide particles with hydratedmetal oxide can be performed by the following method. That is, thetitanium dioxide slurry is subjected to wet grinding and classificationand then, pH is adjusted to 5 or more, preferably 6 or more, morepreferably about 7. Thereafter, to the titanium dioxide slurry are addeda water-soluble aluminum salt and, if necessary, another water-solublemetal salt or water-soluble silicon compound, and subsequently pH of theslurry is changed to precipitate on the surface of titanium dioxidepigment a slightly soluble hydrated aluminum oxide and, if necessary,another slightly soluble hydrated metal oxide. Thus, the titaniumdioxide particles can be surface treated. For example, a representativemethod of the surface treatment using a reaction bath with a stirrer isas follows: A water-soluble alkali solution such as sodium hydroxide orpotassium hydroxide is added to the titanium dioxide slurry obtainedafter subjected to wet grinding and classification steps, thereby toadjust pH of the slurry to 7.0±1.0. To this pH adjusted titanium dioxideslurry are added an aluminate such as an alkali aluminate and, ifnecessary, an aqueous solution of a water-soluble alkali such as sodiumhydroxide or potassium hydroxide. Thereafter, in order to decrease pH ofthe slurry which is alkaline and to precipitate hydrated aluminum oxideon the surface of the titanium dioxide particles, a mineral acid such assulfuric acid or hydrochloric acid or an aqueous solution of a saltwhich reacts as an acid is added to the slurry, thereby to accomplishthe surface treatment.

The thus surface treated titanium dioxide slurry usually has a pH of7.0±1.0. Sodium aluminate is especially useful as alkali aluminates. Itis also possible to carry out the surface treatment with an inorganicsurface treating agent in addition to the aluminate. In this case, theinorganic surface treating agent can be added at any stage before,during and after addition of the aluminate, but it is especiallyadvantageous to add it before addition of the aluminate.

As the inorganic surface treating agents other than the aluminates,there may be used various compounds such as alkali silicates and silicontetrachloride as silicon compounds, titanium tetrachloride as titaniumcompounds and besides, metal compounds of zirconium, zinc, manganese andthe like, and phosphoric acid compounds.

In this case, for example, when hydrated aluminum oxide is used, it isused in an amount of 0.15-1.5% by weight, preferably 0.2-1.2% by weight(in terms of Al₂ O₃) based on the titanium dioxide.

For further increase of sharpness of a printed image formed on theresin-coated paper type photographic support which contains the titaniumdioxide pigment in a resin layer, it is preferred to wash the surfacetreated titanium dioxide pigment with water until the suspensionelectric conductivity defined below reaches 60 μν/cm or less. Thesuspension electric conductivity of titanium dioxide pigment here isdefined as follows. 10.0 g of a titanium dioxide pigment is added to 100ml of distilled water in a beaker of 100 ml in volume and the content inthe beaker is stirred on a magnetic stirrer by stirring power of arotator (rotating rate: 420 rpm) for 16 minutes keeping the liquidtemperature at 21.5° C.±0.5° C. to make a suspension of the titaniumdioxide pigment. 16 minutes after start of the stirring, suspensionelectric conductivity of the suspension of the titanium dioxide pigmentis measured by an electric conductivity meter at 21.5° C.±0.5° C. withstirring. The resulting electric conductivity is defined to be thesuspension electric conductivity of the titanium dioxide pigment in thepresent invention.

The titanium dioxide pigment used advantageously in the presentinvention which has a suspension electric conductivity of 60 μν/cm orless is prepared in the following manner. That is, after the surfacetreatment, the original mother liquor is filtered with a filter pressand subsequently, the titanium dioxide cake in the filter press iswashed with flowing water until a titanium dioxide pigment having asuspension electric conductivity of 60 μν/cm or less is obtained. Thewater washing conditions such as time, amount of water and pressure ofwater can be determined by subjecting the titanium dioxide cakecollected under a series of combinations of experiments to thesuccessive treatments of drying and grinding to prepare a titaniumdioxide pigment and measuring the suspension electric conductivity ofthe titanium dioxide pigment. The washing with water can be carried outin the following manner. The slurry containing titanium dioxide as suchor in the form of suspension obtained by suspending the filter cakeagain in the bath is washed with stored water or flowing water in theform of exchanging of supernatant. The washing with water can be carriedout simultaneously with washing with water in the filter press orseparately. From the point of further increase of sharpness of a printedimage on the photographic support, the titanium dioxide pigment used inthe present invention has a suspension electric conductivity ofpreferably 55 μν/cm or less, more preferably 50 μν/cm or less.

From the point of further increase in sharpness of a printed image onthe resin-coated paper type photographic support containing the titaniumdioxide pigment in a resin layer, it is advantageous to produce thetitanium dioxide pigment by finely grinding by a fluid energy mill thetitanium dioxide cake after being subjected to water washing and drying.As the fluid energy mills, steam mills such as a micronizer areespecially preferred, but air mills may also be used. It is especiallypreferred to carry out the first stage grinding by an impact grindersuch as a hammer mill before grinding by a fluid energy mill and then,the fine grinding by a fluid energy mill as the second stage grinding.

If necessary, the titanium dioxide pigment used in the present inventionmay be treated with various organic compounds such as triethanolamine,trimethylolpropane, metal salts of fatty acids, and organopolysiloxanes.

As antioxidants used in the present invention, there may be used variousantioxidants such as phenolic type, amine type and phosphate ester typeas far as they cause no problems when contained in the resin compositionwhich constitutes a resin layer provided on the side of the resin-coatedpaper type photographic support on which images are to be formed.However, hindered phenol type antioxidants are especially preferredbecause they give no adverse effect on the photographic emulsion layerand they can more effectively inhibit die lip stain. As these preferredhindered phenol type antioxidants, mention may be made of, for example,1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,tetrakis[methylene(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate)]methane,octadecyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate,2,2',2"-tris[(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy]ethylisocyanurate,1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-di-methylbenzyl)isocyanurate,tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenylenediphosphite ester,4,4'-thiobis-(6-tert-butyl-o-cresol),2,2'-thiobis-(6-tert-butyl-4-methylphenol),tris-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,2,2'-methylene-bis-(4-methyl-6-tert-butylphenl),4,4-methylene-bis-(2,6-di-tert-butylphenol),4,4'-butylidenebis-(3-methyl-6-tert-butylphenol),2,6-di-tert-butyl-4-methylphenol,4-hydroxy.methyl-2,6-di-tert-butylphenol, and2,6-di-tert-4-n-butylphenol. The antioxidants may also be used incombination of two or more depending on characteristics of theantioxidants used.

Content of the antioxidant in the polyolefin resin composition ispreferably 10-1000 ppm, more preferably 20-500 ppm by weight of theresin composition. When content of the antioxidant is less than 5 ppm ormore than 1000 ppm, die lip stain readily occurs and especially, when itis more than 1000 ppm, adhesion between the substrate and the resinlayer tends to be inferior.

Incorporation of the antioxidant into the resin composition can becarried out by using so-called compound which comprises a polyolefinresin in which the antioxidant is previously contained, by using asuitable amount of a resin in which the antioxidant is contained at arelatively high concentration, or by adding the antioxidant at the timeof preparation of the resin composition by a kneader. The above methodscan be suitably combined depending on kind and content of theantioxidant used.

As the thermoplastic resins used in the present invention, there may beused any of those which can be coated to form a resin film on asubstrate paper and examples thereof are homopolymers such aspolyolefins, polystyrenes, polyvinyl chloride, polyacrylic esters,linear polyesters (e.g., polyethylene terephthalate), polyamides (e.g.,nylon), cellulose esters, and polyacrylonitriles; copolymers such asethylene-vinyl acetate copolymers; and mixtures thereof. Preferred arethermoplastic resins such as polyolefins, polystyrenes, polyethyleneterephthalate, and polyvinyl chloride. Especially preferred arepolyolefin resins from the points of cost and their superior extrusioncoatability and adhesion to a substrate paper.

The polyolefin resins used in the present invention include, forexample, homopolymers such as polyethylene, polypropylene, polybutene,and polypentene; copolymers comprising two or more of α-olefins such asethylene-propylene copolymer and ethylenebutylene copolymer; andmixtures thereof. Among them, polyethylene resins are especiallypreferred from the point of melt coatability and from economical viewpoint. The polyethylene resins include, for example, low-densitypolyethylenes, medium-density polyethylenes, high-density polyethylenes,straight-chain low-density polyethylenes, copolymers of ethylene andα-olefins such as propylene and butylene, carboxy-modified polyethylenesand mixtures thereof. These may have various densities, melt flow rates(hereinafter referred to as "MFR"), molecular weights, and molecularweight distributions. Normally, those which have a density of 0.90-0.97g/cm³, an MFR of 1-30 g/10 min, preferably 3-15 g/10 min and a molecularweight of 20,000-250,000 may be used singly or in admixture of two ormore. When the resin layer comprises multi-layer, resins of differentproperties and construction can be used for respective layers, namely, aresin having an MFR of, for example, 5-20 g/10 min can be used as theuppermost layer and a resin having an MFR of, for example, 2-10 g/10 mincan be used as a lower layer.

In order to contain the titanium dioxide pigment in the resin layer ofthe resin-coated paper type photographic support, there may be usuallyemployed a method of using a so-called masterbatch, which is a resincomposition prepared previously by mixing the titanium dioxide pigmentwith a diluent polyolefin resin to a desired concentration, or using aso-called compound, in which the titanium dioxide pigment is thoroughlymixed with a polyolefin resin at a desired concentration from the start.These masterbatch and compound are usually prepared by a Banbury mixer,a kneader, an extruder for kneading, a twin-roll mill, a three-rollmill, and the like. Of these, the Banbury mixer and the extruder forkneading are advantageously used. These kneading machines may be used incombination of two or more.

In order to improve releasing characteristics of the polyolefin resinlayer from cooling roll in production of the resin-coated paper typephotographic support, it is preferred to contain a metal salt of a fattyacid in the resin layer of the photographic resin-coated paper by addingthe metal salt of fatty acid to a mixture of the polyolefin resin andthe titanium dioxide pigment when they are processed into themasterbatch or compound of the titanium dioxide pigment. As the metalsalt of fatty acid, there may be mentioned, for example, zinc stearate,calcium stearate, aluminum stearate, magnesium stearate, zirconiumoctylate, sodium palmitate, calcium palmitate, and sodium laurate.Addition amount of the salt is preferably 0.1-50% by weight based on thetitanium dioxide pigment and 0.01-5% by weight based on the resin layercontaining the titanium dioxide pigment.

When content of the titanium dioxide pigment in the resin layer of theresin-coated paper type photographic support in the present invention isless than 7% by weight based on the resin, sharpness of the printedimage formed on the photographic support is insufficient. When itexceeds 35% by weight, the resin composition becomes less flowable sothat it cannot be extruded properly, or it brings about increased dielip stain. Especially preferable content is 9-30% by weight.

It is preferred to contain a fluorescent agent in the resin layer of theresin-coated paper type photographic support in order to reduceyellowness caused by the titanium dioxide pigment, especially when thetitanium dioxide pigment is contained at a high concentration in theresin layer for obtaining especially high sharpness. As the fluorescentagents, there may be used various ones such as naphthalene type,stilbene type, thiophene type and coumarin type, butbis(benzoxazolyl)naphthalene type and/or bis(benzoxazolyl)stilbene typefluorescent agents having a substituting group are preferred from thepoints of improvement of whiteness, dispersibility in the polyolefinresin, heat resistance, bleed-out resistance, weathering resistance andstability in photographic processing solution of the fluorescent agent.Examples of these preferable naphthalene type fluorescent agents andstilbene type fluorescent agents are those which are represented by thefollowing formulas. For naphthalene type fluorescent agents, preferredare those which have a substituting group having 6 or more carbon atomsconsidering the bleed-out resistance. ##STR1##

The fluorescent agent can be contained in the polyolefin resincomposition by adding it during a step of preparing masterbatch orcompound of the titanium dioxide pigment to make a masterbatch or acompound which comprises the titanium dioxide pigment, the fluorescentagent, the polyolefin resin, and the dispersing agent such as a metalsalt of fatty acid.

The fluorescent agent can also be contained in the resin composition inthe following manner. That is, the fluorescent agent is preliminarilymixed with a low molecular weight polyolefin which is solid at roomtemperature and is lower than the main polyolefin resin in softeningpoint and/or a dispersing agent such as a metal salt of fatty acid, andthe resulting mixture is dispersed in the main polyolefin resin to makea fluorescent agent masterbatch, thereby to contain the fluorescentagent in the resin composition. Content of the fluorescent agent in theresin layer of the photographic support is preferably 0.3-30 mg/m², morepreferably 0.5-10 mg/m², from overall view points of whiteness,processability of the resin, bleed-out resistance and the like.

It is preferred to contain inorganic or organic, blue pigments or bluedyes in the resin layer of the resin-coated paper type photographicsupport of the present invention, thereby to further enhance theapparent whiteness of the support. Examples of these pigments and dyesinclude cobalt blue, Prussian blue, and ultramarine as inorganiccompounds ad cerulean blue, phthalocyanine blue, Chromophthal Blue A3Ras organic compounds. Addition amount of the pigments or dyes is0.025-0.5% by weight, preferably 0.05-0.2% by weight of the resin layerfor inorganic blue pigments, and 0.001-0.1% by weight, preferably0.0025-0.05% by weight of the resin layer for organic blue compounds.When the amount is too small, coloration cannot be attained and when itis too large, not only lightness reduces, but also die lip stain occursmuch.

Furthermore, it is advantageous to contain, if necessary, inorganic ororganic magenta pigments or magenta dyes in the resin layer of theresin-coated paper type photographic support. Examples thereof arecobalt violet, fast violet, manganese violet, reddish ultramarine andquinacridone red. Addition amount thereof is 0.025-1.0% by weight,preferably 0.1-0.4% by weight of the resin layer for inorganic magentapigments, and 0.001-0.3% by weight, preferably 0.002-0.015% by weight ofthe resin layer for organic magenta compounds.

The resin-coated paper type photographic support of the presentinvention has a resin layer which contains the titanium dioxide pigmentand antioxidant and, more preferably, the above-mentioned metal salt offatty acid, fluorescent agent, and inorganic or organic coloring pigmentor coloring dye. When the resin layer comprises multi-layer, theabove-mentioned titanium dioxide pigment, antioxidant, metal salt offatty acid, fluorescent agent, and coloring pigment or dye may also becontained in the additional resin layer in addition to the resin layerof the present invention. Moreover, the resin layer on the image-formingside of the photographic support and the resin layer on the oppositeside of the support may preferably contain, in addition to the abovetitanium dioxide pigment, antioxidant, metal salt of fatty acid,fluorescent agent, and coloring pigment or dye, various additives, e.g.,white pigments such as titanium dioxide other than that of the presentinvention, zinc oxide, talc, and calcium carbonate; fatty acid amidessuch as stearic acid amide and arachidic acid amide; organosiliconecompounds such as polyorganosiloxane; and ultraviolet absorbers such asTinuvin 320, Tinuvin 326 and Tinuvin 328 (trade name of Ciba-Geigy Co.,Ltd.) in optional combination.

The photographic support prepared in this invention is produced by aso-called extrusion coating method, in which the molten thermoplasticresin, preferably the polyolefin resin is casted on the running sheet tocoat usually both sides of the substrate such as paper, synthetic paperor a film with the resin. In order to form a resin layer having amultilayer structure, preferably used is a so-called tandem extrusionsystem, in which the inner resin layer and the outermost resin layer onthe front side of the photographic support are successively, preferablycontinuously, formed by extrusion coating or a so-called coextrusioncoating system, in which the outermost resin layer and the inner resinlayer are simultaneously formed by extrusion coating. Before thesubstrate is coated with the resin, the substrate is preferablysubjected to an activating treatment such as a corona dischargetreatment, a flame treatment or the like. The emulsion-layer side of thephotographic support has a glossy surface, a finely toughened or mattesurface to such an extent that it does not affect the gloss of thesurface of the photographic paper obtained therefrom disclosed inJapanese Patent Application Kokai No. 55-26507, a silky surface or thelike. Usually, the back side of the photographic support has a dullsurface. The front side or, if necessary, both sides of the photographicsupport may be subjected to an activating treatment such as a coronadischarge treatment, a flame treatment or the like. The photographicsupport may be further subjected to an subbing treatment as disclosed inJapanese Patent Application Kokai No. 61-84634 after the activatingtreatment. The thickness of the resin layer on the front or back side isnot critical; however, in general, it is preferably 10-50 μm.

The substrate used in this invention includes a natural pulp papermainly composed of natural pulp; a synthetic fiber-containing papercomposed of natural pulp and a synthetic fiber; a synthetic fiber papermainly composed of a synthetic fiber; a so-called synthetic paperproduced by making a film composed of a synthetic resin such aspolystyrene, polypropylene or the like into a paper form; and a filmcomposed of cellulose acetate, poly(ethylene terephthalate),polycarbonate or the like. As the substrate for a polyolefinresin-coated paper, the natural pulp paper (hereinafter referred to as"base paper") is advantageously used in view of the objects of thisinvention of providing economically a photographic support which attainsa print excellent in image sharpness, in which substantially nomicrogrits or streaks due to the die lip stain appear, and whichtherefore has excellent surface property.

As a pulp composing the base paper used in this invention,advantageously used is a natural pulp appropriately selected asdisclosed in Japanese Patent Application Kokai Nos. 58-37642, 60-67940,60-69649, 61-35442 and the like. However, if necessary, synthetic pulpor synthetic fiber may be used along with the natural pulp. As thenatural pulp, preferably used is a wood pulp such as softwood pulp,hardwood pulp or a mixture thereof, which has been subjected to usualbleaching with chlorine, hypochlorite, chlorine dioxide or the like;alkali extraction or alkali treatment; oxidation bleaching with hydrogenperoxide, oxygen or the like; or a combination of these treatments.Moreover, various pulps may be used such as kraft pulp, sulfite pulp,soda pulp and the like.

Into the base paper used in this invention may be incorporated varioussizing agents or polymer in the preparation of a slurry of the paperstock.

Sizing agents for the base paper preferably used in this inventioninclude metal salts of fatty acids, fatty acids, alkylketene dimers,alkenyl- or alkyl-succinic anhydrides, epoxized amides of higher fattyacids as disclosed in Japanese Patent Application Kokai No. 54-147211and organic fluoro compounds as disclosed in Japanese Patent ApplicationKokai No. 56-109343.

The sizing agent suitable for the base paper used in this inventionincludes metal salts of fatty acids and fatty acids in such a form thatthey can be fixed to pulp using a water-soluble aluminum salt such asaluminum chloride, sulfite alumina, poly(aluminium chloride) or thelike; alkylketene dimers in such a form that they can be fixed with orwithout the water-soluble aluminium salt and a combination of thealkylketene dimer and an epoxized amide of a higher fatty acid. Themetal salts of higher fatty acids and the fatty acids are preferablythose having 12-22 carbon atoms and they are preferably added in anamount of 0.5-4.0% by weight based on the bone-dry weight of the pulp.The proportion of the solid weight of the water-soluble aluminium saltoptionally added to the weight of the sizing agent is preferably1/20-4/1, more preferably 1/10-1/1. The alkyl group of the alkylketenedimers has preferably 8-30 carbon atoms, more preferably 12-18 carbonatoms. Usually, alkylketene dimers are available on the market in theform of an emulsion, a specific example of which is Aquapel 360XC (atrade name of Dic Hercules Chemicals. Inc.). They are added preferablyin an amount of 0.2-4.0% by weight based on the bone-dry weight of thepulp.

The high molecular weight compound advantageously added to the basepaper used in this invention in the stock preparation includes acationic wet-strength-reinforcing agent or a cationic, anionic oramphoteric strength-reinforcing agent. The cationicwet-strength-reinforcing agent is preferablypolyamine-polyamide-epichlorohydrin resin and it is added in an amountof preferably 0.05-4.0% by weight, more preferably 0.15-1.5% by weight,based on the dry weight of the pulp. Specific examples of the cationicwet-strength-reinforcing agent are Kymene 557H, kymene S-25, EpinoxP-130 (these are trade names of Dic Hercules Chemicals. Inc.) and thelike.

The cationic, anionic and amphoteric strength-reinforcing agents includecationized starch as disclosed in Japanese Patent Application Kokoku60-17103; cationic poly(vinyl alcohol) as disclosed in Japanese PatentApplication Kokai No. 63-214748; cationic polyacrylamide as disclosed inJapanese Patent Application Kokai Nos. 57-185432 and 57-197539; anionicpolyacrylamide as disclosed in Japanese Patent Application Kokoku Nos.62-23119 and 62-31118; amphoteric polyacrylamide as disclosed inJapanese Patent Application Kokoku No. 61-37613 and Japanese PatentApplication Kokai No. 59-31949; vegetable galactomannan as disclosed inJapanese Patent Application Kokai No. 59-125731; and the like. They areadded in an amount of preferably 0.05-8% by weight, more preferably0.15-4% by weight, based on the dry weight of the pulp.

To the base paper used in this invention may be added various additivesin the preparation of the paper slurry. There may be added, in propercombination, a filler such as clay, kaolin, potassium carbonate, bariumsulfate, magnesium silicate, titanium dioxide or the like; a pH modifiersuch as sodium hydroxide, sodium carbonate or the like; a coloringpigment, a coloring dye or a fluorescent whitening agent as disclosed inJapanese Patent Application Kokai No. 54-147033 and Japanese PatentApplication Kokai Nos. 63-204251 and 1-266537.

To the base paper used in this invention may be added variouswater-soluble polymers, antistatic agents, latices, emulsions, pigments,pH modifiers and the like by spraying or tab size pressing. Thewater-soluble polymer includes starchy polymers as disclosed in JapanesePatent Application Kokai No. 1-266537, poly(vinyl alcohol)-typepolymers, gelatinic polymers, polyacrylamide-type polymers, cellulosicpolymers and the like. The antistatic agent includes alkali metal saltssuch as sodium chloride, potassium chloride and the like as disclosed inJapanese Patent Application Kokai No. 1-266537; alkaline earth metalsalts such as calcium chloride, barium chloride and the like; colloidalmetal oxides such as colloidal silica and the like; organic antistaticagents as disclosed in Japanese Patent Application Kokai No. 58-82242;and the like. The latices and emulsions include petroleum resin emulsionand latices of styrene/acrylic acid/acrylic acid ester terpolymer,styrene/acrylic acid/butadiene terpolymer, ethylene/vinyl acetatecopolymer, styrene/maleic acid/acrylic acid ester terpolymer and thelike. The pigment includes clay, kaolin, talc, barium sulfate, titaniumdioxide and the like. The pH modifier includes hydrochloric acid,phosphoric acid, citric acid, sodium hydroxide, sodium carbonate and thelike. These are advantageously used in appropriate combination with thecoloring pigment, coloring dye or fluorescent agent mentioned above.

In order to make the base paper used in this invention, there may beused a conventionally used paper machine such as Fourdrinier machine, acylinder machine or the like; however, it is advantageous to adopt anappropriate method for making paper as disclosed in Japanese PatentApplication Kokai Nos. 58-37642, 61-260240 and 61-284762. Though thethickness of the base paper is not critical, the base paper ispreferably treated by a calender after the base paper is made as shownin Japanese Patent Application Kokai Nos. 58-37642 and 60-126397. Thebasis weight of the base paper is preferably 40-250 g/m².

For the purpose of the prevention of static electrification, curling orthe like, various backcoats layers may additionally be applied to thephotographic support of this invention. The backcoat layers may containin appropriate combination an inorganic antistatistic agent, an organicantistatistic agent, a hydrophilic binder, a latex, a hardening agent, apigment, a surfactant and the like as disclosed in Japanese PatentApplication Kokoku Nos. 52-18020, 57-9059, 57-53940, 58-56859; JapanesePatent Application Kokai Nos. 59-214849 and 58-184144; and the like.

The photographic support obtained in this invention is further appliedwith various photograph-constituting layers and can be applied to avariety of uses such as a color photographic paper, a monochromicphotographic paper, a phototype-setting photographic paper, a copyphotographic paper, a reversal photographic material, a negative andpositive photographic material for silver salt dispersion transfer, aprinting material and the like. As example of the photographic layers,there can be mentioned a photographic emulsion layer of silver chloride,silver bromide, silver chlorobromide, silver iodobroide, silverchloroiodobromide or the like. The photographic emulsion layercontaining a silver halide may contain color couplers to form a silverhalide constituting layer having a multilayer structure. The emulsionlayer may contain a physical developing nucleus to form a receivinglayer for silver salt dispersion transfer.

As a binder of these photographic layers, there may be used ahydrophilic polymer such as poly(vinyl pyrrolidone), poly(vinylalcohol), a sulfuric acid ester of a polysaccharide or the like inaddition to a conventional gelatin. The photographic layer may containvarious additives. For example, there may be contained, in appropriatecombination, an optical sensitizing dye such as a cyanine dye, amerocyanine dye or the like; a chemical sensitizer such as awater-soluble gold compound, a sulfur compound or the like; anantifoggant or a stabilizer such as a hydroxytriazolopyrimidinecompound, a mercaptoheterocyclic compound or the like; a hardening agentsuch as formaldehyde, a vinylsulfone compound, an aziridine compound orthe like; an auxiliary agent for coating such as a salt ofbenzensulfonic acid, a salt of sulfosuccinic acid or the like; ananti-contaminant such as a dialkylhydroquinone compound or the like;other components such as a fluorescent whitening agent, a dye forimproving the sharpness, an antistatic agent, a pH modifier, a foggingagent, or a water-soluble iridium or rhodium compound in the productionor dispersion of a silver halide.

The photographic material containing a silver halide obtained from thephotographic support produced in this invention is subjected totreatments such as exposure, development, termination, fixing, bleach,stabilization and the like as shown in "Photosensitive Materials forPhotography and Handling Thereof" by Goro Miyamoto, published byKyoritsu Shuppan Co., Ltd., Photographic Techniques Course Vol. 2,depending upon the photographic material thereof.

Especially, the multi-layered silver halides color photographic materialcan be processed in a color development bath containing any kind of adeveloping agent such as CD-III, CD-IV (these two compounds are productsof Kodak Co., Ltd.), Droxychrom (a trade name of May & Bayker Co., Ltd.)or the like, and further processed in a single bleaching-fixing bath.The developing solution in the bath contains the developing agent andmay also contain a development accelerator such as benzyl alcohol, athallium salt, phenidone or the like, or the solution may be of a typecontaining substantially no benzyl alcohol. A useful single bathbleaching-fixing liquid is a solution of a metal salt ofaminopolycarboxylic acid (e.g. a complex ferric salt ofethylenediaminetetraacetic acid, propylenediaminetetraacetic acid,etc.), and a useful fixing agent contained therewith is e.g. sodiumthiosulfate, ammonium thiosulfate or the like; the solution may furthercontain a variety of additives, for example, a desilver accelerator(e.g. mercaptocarboxylic acid as disclosed in U.S. Pat. No. 3,512,979, amercaptoheterocyclic compound as disclosed in Belgian Patent No.682,426, etc.), an anticontaminant, a pH modifier, a pH buffering agent,a hardening agent (e.g. magnesium sulfate, aluminium sulfate, potassiumalum, etc.), a surfactant and the like. While pH of such singlebleaching-fixing bath liquid may vary, a useful pH range is 6.0-8.0.

The following Examples further illustrate the invention.

EXAMPLE 1

Titanium dioxide was subjected to hydrolysis and washing in theproduction process for rutile type titanium dioxide pigment according tosulfuric acid method mentioned in this specification and then wasconcentrated by a filter. The thus concentrated titanium dioxide was putin a kneader and a predetermined amount of magnesium sulfate was addedthereto, followed by well stirring. Then, the mixture was subjected tocalcination under predetermined conditions so that diameter of titaniumdioxide particle was as shown in Table 1. The resulting rutile typetitanium dioxide clinker was subjected to grinding and dressing ofgrains and besides to wet grinding and classification to obtain titaniumdioxide slurry substantially free from coarse particles.

Amount of magnesium compound on the surface of titanium dioxideparticles in mentioned this specification is one obtained analyticallyby the following method.

1.0000 g of titanium dioxide clinker sample is accurately weighed andput in a crucible. Thereto is added 10 ml of a special grade 36 wt %hydrochloric acid solution. The crucible is closed and the content isheated at 360° C.±20° C. for 15 minutes on a sand bath and cooled andthen is filtrated (if the filtration is incomplete, centrifugalseparation is employed in combination) and then, is washed with 10 ml ofa dilute hydrochloric acid obtained by diluting 10 ml of special grade36 wt % hydrochloric acid solution with 490 ml of distilled water. Tothe resulting filtrate is added 3 ml of 3% by weight solution of specialgrade SrCl₂.6H₂ O in distilled water and total amount is adjusted to 100ml with distilled water. This is used as a test solution. This testsolution is subjected to atomic-absorption spectroscopy andconcentration of magnesium in the test solution is calculated bypreviously obtained calibration curve. Thus, amount of magnesiumcompound present on the surface of titanium dioxide particles isdetermined.

The above slurry was introduced into an acid washing tank and then,dilute sulfuric acid was added thereto to adjust to pH 1.0 and to carryout acid-washing. A sample prepared without addition of dilute sulfuricacid was employed as a control sample. The acid-washing was carried outby the stored water method. The slurry temperature at acid-washing waskept at 45° C. and acid-washing with stored water for 30 minutes wasrepeated three times.

Thereafter, pH of the slurry was raised to about 9.2 with sodiumhydroxide and temperature of the slurry was adjusted to about 70° C. andthen, to the slurry was added an aqueous sodium aluminate solution in anamount of 0.5% by weight in terms of Al₂ O₃ based on the dry titaniumdioxide and this was left to stand for 30 minutes.

Then, pH of the slurry was lowered to 7.0 with addition of 20% sulfuricacid and the slurry was aged for 2 hours. Thereafter, the originalmother liquor of the titanium dioxide slurry surface-treated with sodiumaluminate was filtered by a filter press and subsequently, the titaniumdioxide cake in the filter press was washed with flowing water under thepredetermined water washing conditions until the suspension electricconductivity of the titanium dioxide pigment defined above reached 50μν/cm.

The titanium dioxide cake was dried and impact ground by a hammer millwith a quantitative feeder and furthermore was subjected to thefinishing grinding in a steam mill to produce the titanium dioxidepigments mentioned in Table 1.

50 parts by weight of each of the resulting titanium dioxide pigment, 50parts by weight of low-density polyethylene (MFR=7, density 0.923g/cm³), and 2.5 parts by weight of zinc stearate were well kneaded at150° C. by a Banbury mixer to obtain a masterbatch of the above titaniumdioxide pigment.

A mixture of 50 parts by weight of bleached hardwood kraft pulp and 50parts by weight of bleached softwood sulfite pulp was beaten to aCanadian standard freeness of 310 ml and thereto were added, based on100 parts by weight of the pulp, 3 parts by weight of cationized starch,0.2 part by weight of anionized polyacrylamide, 0.4 part by weight (asketene dimer content) of an alkylketene dimer emulsion, 0.4 part of apolyamino-polyamide-epichlorohydrin resin. From the resulting paperstock, a paper of 160 g/m² in basis weight was made and this wet paperwas dried at 110° C. Then, successively the paper was impregnated in aproportion of 25 g/m² with an impregnating solution comprising 3 partsby weight of carboxy-modified polyvinyl alcohol, 0.05 part by weight ofa fluorescent brightener, 0.002 part by weight of a blue dye, 0.2 partby weight of citric acid, and 97 parts by weight of water, dried with ahot air of 110° C., and was further subjected to supercalendering undera linear pressure of 90 kg/cm. Thereafter, both sides thereof weresubjected to corona discharge treatment to make a base paper ready forbeing coated with resin to make a photographic support.

Next, the back side of the base paper was coated with a 1:1 mixture of ahigh-density polyethylene (density 0.960 g/cm³, MFR=5) and a low-densitypolyethylene (density 0.923 g/cm³, MFR=5) at a thickness of 30μ at aresin temperature of 330° C. by a melt extrusion coater. Then, the frontside of the base paper was coated with a resin composition comprising 30parts by weight of the above masterbatch of titanium dioxide pigment, 20parts by weight of a high-density polyethylene (density 0.960 g/cm³,MFR=5), and 50 parts by weight of a low-density polyethylene (density0.923 g/cm³, MFR=5) at a thickness of 30μ at a resin temperature of 330°C. to make a polyethylene resin-coated paper containing the titaniumdioxide pigment. In this case, the surface of the polyethylenecontaining the titanium dioxide pigment was processed to a glossysurface and the surface of the polyethylene on the back side wasprocessed to a matte surface like paper.

The number of microgrit formed on the surface of the polyethylene resincontaining the titanium dioxide pigment of the thus obtainedpolyethylene resin-coated paper was visually counted.

Die lip stain was evaluated in the following manner.

The polyethylene resin composition containing the titanium dioxidepigment was melt extruded using a screw type extrusion machine having anextrusion bore of 65 mm and a T-die of 750 mm width at a resintemperature of 320° C. and at a screw revolution speed of 100 rpm for 2hours. Then, the number of stain generated at die lip was-counted.

Next, in order to make comparison on sharpness of a printed image, acolor photographic paper having the above obtained photographic supportwas made. First, the back side of the photographic support was subjectedto corona discharge treatment and then was coated with 0.4 g/m² of abackcoat layer comprising colloidal silica and styrene/acrylic latex ata dry weight ratio of 1:1. Then, the resin layer containing the titaniumdioxide pigment on the front side of the photographic support wassubjected to corona discharge treatment and then coated with ablue-sensitive emulsion layer containing yellow-coloring coupler, anintermediate layer containing an anti-color mixing agent, agreen-sensitive emulsion layer containing a magenta-coloring coupler, anultraviolet absorbing layer containing an ultraviolet absorber, ared-sensitive emulsion layer containing a cyan-coloring coupler, and aprotective layer to make a color photographic paper. Eachcolor-sensitive emulsion layer contained 0.6 g/m² of silverchlorobromide in terms of silver nitrate and further contained gelatinnecessary for preparation, dispersion and film-formation of silverhalide and besides, an antifoggant, a sensitizing dye, a coating aid, ahardener, a thickner and a filter dye in a proper amount.

A resolving power chart was brought into close contact with thephotographic paper obtained above. This assembly was exposed to greenlight and the exposed photographic paper was subjected to colordevelopement to obtain a test sheet. Sharpness of the image formed onthe test sheet was visually evaluated. Criteria for the evaluation areas follows:

⊚: Very good

◯: Good

: Fairly good

Δ: Fairly bad

                                      TABLE 1                                     __________________________________________________________________________              Amount of magnesium                                                                              Particle diameter of                                                                     The number                            Sample    oxide in clinker                                                                         Acid-washing                                                                          titanium dioxide                                                                         of microgrit                                                                         Total number of die            No.       (note 1)   step    pigment (μm) (note 2)                                                                 (/m.sup.2)                                                                           lip stain (Note                                                                         Sharpness            __________________________________________________________________________    The present                                                                          2  2.01 % by weight                                                                         Carried out                                                                           0.110      3.6     5        ◯        invention                                                                            3  1.04       "       0.115      1.4     5        ⊚                                                              1                           4  0.55       "       0.120      0.9     3        ⊚                                                              1                           5  0.10       "       0.127      0.5     1        ⊚                                                              8                           6  0.021      "       0.134      0.6     1        ⊚                                                              .                           7  0.012      "       0.149      0.6     2        ◯        Outside the                                                                          8  0.0058     "       0.162      0.7     2        Δ              present                                                                              1  2.48       "       0.102      7.1    12        Δ              invention                                                                     Outside the                                                                         11  2.48       Not carried out                                                                       0.102      30     28        Δ              present                                                                             12  2.01       "       0.110      24     20        ◯        invention                                                                           13  1.04       "       0.115      20     18        ⊚           14  0.55       "       0.120      16     14        ⊚           15  0.10       "       0.127      14     12        ⊚           16  0.021      "       0.134      12     11        ⊚           17  0.012      "       0.149      13     10        ◯              18  0.0058     "       0.162      13     11        Δ              __________________________________________________________________________     (Note 1): Percent by weight in terms of MgO based on the dry titanium         dioxide.                                                                      (Note 2): The numberaverage diameter defined in this specification.           (Note 3): Total number of die li stain which occurred on the front side       and the rear side of the die.                                            

As is clear from Table 1, when the titanium dioxide pigment contained inthe resin layer on the image forming side of the resin-coated paper typephotographic support had an analytical value of magnesium of titaniumdioxide clinker corresponding to the titanium dioxide pigment of2.01-0.012% by weight in terms of magnesium oxide based on the titaniumdioxide and was prepared through the acid-washing step and had aparticle diameter of 0.110-0.149 μm, both the die lip stain and themicrogrit occurred a little and besides, sharpness of a printed imageformed was good. However, even if the titanium dioxide pigment wasprepared through the acid-washing step, when analytical value of theclinker was 2.48% by weight in terms of magnesium oxide and particlediameter of the titanium dioxide pigment was 0.102 μm, both the die lipstain and the microgrit occurred somewhat much. Similarly, when amountof magnesium oxide was 0.0058% by weight and particle diameter of thetitanium dioxide pigment was 0.162 μm, both the die lip stain and themicrogrit occurred a little, but sharpness of a printed image wassomewhat inferior.

On the other hand, even if amount of magnesium oxide based on thetitanium dioxide and particle diameter of the titanium dioxide pigmentare both within the scope of the present invention, when the titaniumdioxide pigment was prepared without the acid-washing step, both the dielip stain and the microgrit occurred much and there is practicalproblem.

EXAMPLE 2

The same procedure as in Example 1 was repeated, except that thefollowing composition was used as the resin composition containing thetitanium dioxide pigment on the front side of the photographicresin-coated paper.

First, 50 parts by weight of a low-density polyethylene (density 0.918g/cm³, MFR=7) to whichtetrakis[methylene(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate)]methaneas an antioxidant was previously added so that it was contained in suchan amount as shown in Table 2, 50 parts by weight of a rutile typetitanium dioxide pigment which was the same as of Sample No. 3 or No. 13mentioned in Table 1, and 2.5 parts by weight of zinc stearate were wellkneaded by a Banbury mixer at 150° C. to prepare a masterbatch of thetitanium dioxide pigment containing the antioxidant.

Separately, 0.28 part by weight of fluorescent agent [IX] mentionedhereabove and 0.28 part by weight of zinc stearate were previously wellmixed. The resulting mixture and 40 parts by weight of the samelow-density polyethylene as used for preparation of the above titaniumdioxide pigment masterbatch were well kneaded in a Laboplastomill at135° C. to prepare a fluorescent agent masterbatch.

Except for Sample No. 29 in Table 2, 30 parts by weight of the abovetitanium dioxide pigment masterbatch, 20 parts by weight of ahigh-density polyethylene (density 0.960 g/cm³, MFR=5), and 50 parts byweight of a low-density polyethylene (density 0.923 g/cm³, MFR=5) wereblended to obtain a resin composition for front side of the photographicsupport.

For Sample No. 29, 30 parts by weight of the above titanium dioxidepigment masterbatch, 20 parts by weight of a high-density polyethylene(density 0.960 g/cm³, MFR=5), 47 parts by weight of a low-densitypolyethylene (density 0.923 g/cm³, MFR=5), and 3 parts by weight of theabove masterbatch containing the fluorescent agent were blended and theblend was used as a resin composition for front side of the photographicsupport.

The results obtained are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________              Kind of titanium Amount of                                                    dioxide pigment  antioxidant                                                                         Presence of                                                                         The number                                                                           Total                           Sample    in resin layer                                                                         Acid-washing                                                                          (ppm) fluorescent                                                                         of microgrit                                                                         number of   Apparent            No.       (Note 4) step    (Note 5)                                                                            agent (/m.sup.2)                                                                           die lip stain                                                                       Sharpness                                                                           whiteness           __________________________________________________________________________    The present                                                                         21  No. 3    Carried out                                                                           0     No    1.4    5     ⊚                                                                    ◯       invention                                                                           22  "        "       10    "     1.2    2     ⊚                                                                    ◯             23  "        "       20    "     1.0    0     ⊚                                                                    ◯             24  "        "       150   "     0.8    0     ⊚                                                                    ◯             25  "        "       300   "     0.9    0     ⊚                                                                    ◯             26  "        "       500   "     0.9    2     ⊚                                                                    ◯             27  "        "       1000  "     0.8    5     ⊚                                                                    ◯             28  "        "       2000  "     0.9    9     ⊚                                                                    ◯             29  "        "       150   Yes   0.8    0     ⊚                                                                    ⊚    Outside the                                                                         30  No. 13   Not carried out                                                                       0     No    20     18    ⊚                                                                    ◯       present                                                                             31  "        "       150   No    17     15    ⊚                                                                    ◯       invention                                                                     __________________________________________________________________________     (Note 4): The same titanium dioxide pigment as used in Sample No. 3 or No     13 shown in Table 1 of Example 1.                                             (Note 5): Addition amount of antioxidant in the resin composition on the      front side (imageforming side) of the support.                           

It can be seen from Table 2 that generation of die lip stain was highlyinhibited by adding a proper amount of the antioxidant to the resincomposition containing the titanium dioxide pigment used in Sample No. 3(amount of magnesium oxide in the clinker: 1.04% by weight of titaniumdioxide; particle diameter of the titanium dioxide pigment: 0.115 μm;with acid-washing).

Addition amount of the antioxidant is preferably 10-500 ppm, morepreferably 20-300 ppm based on the resin composition. When it is morethan 1000 ppm, die lip stain tends to increase and besides, adhesionbetween the base paper and the resin layer deteriorates.

The samples shown in Table 2 were all superior in sharpness of a printedimage, but Sample No. 29, which corresponds to Sample No. 24 in which aspecific fluorescent agent was additionally contained, was furtherimproved in visual whiteness and had very good quality as a photographicsupport.

In contrast with the above, it can be seen that generation of die lipstain was not inhibited so much even when a proper amount of theantioxidant was added to the resin composition containing the titaniumdioxide pigment used in Sample No. 13 of Table 2 (amount of magnesiumoxide in clinker: 1.04% by weight of the titanium dioxide; particlediameter of the titanium dioxide pigment: 0.115 μm; withoutacid-washing). See Sample No. 30 and Sample No. 31.

EXAMPLE 3

A titanium dioxide pigment was prepared in the same manner as in Example1, except that barium chloride was used in place of magnesium sulfate ina predetermined amount. Photographic supports were made using thetitanium dioxide in the same manner as in Example 1.

The results obtained are shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________              Amount of barium                                                                       Particle diameter                                                    chloride in clinker                                                                    of titanium              Total                             Sample    (% by weight)                                                                          dioxide pigment                                                                        Acid-washing                                                                          The number of                                                                         number of                         No.       (Note 6) (μm)  step    microgrit (/m.sup.2)                                                                  die lip stain                                                                       Sharpness                   __________________________________________________________________________    The present                                                                         42  1.78     0.114    Carried out                                                                           1.6      4    ⊚            invention                                                                           43  0.51     0.125    "       0.6      1    ⊚                  44  0.025    0.138    "       0.7      1    ⊚            Outside the                                                                         45  0.0044   0.167    "       0.7      2    Δ                     present                                                                             41  2.91     0.101    "       8.8     15    Δ                     invention                                                                     Outside the                                                                         51  2.91     0.101    Not carried out                                                                       35      31    Δ                     present                                                                             52  1.78     0.114    "       22      20    ⊚            invention                                                                           53  0.51     0.125    "       18      16    ⊚                  54  0.025    0.138    "       15      14    ⊚                  55  0.0044   0.167    "       17      15    Δ                     __________________________________________________________________________     (Note 6): Percent by weight in terms of BaO based on titanium dioxide on      the dry basis.                                                           

As can be seen from Table 3, occurrence of die lip stain and microgritas well are restrained and sharpness of a printed image was satisfactorywhen the barium analytical value of titanium dioxide clinkercorresponding to the titanium dioxide pigment contained in the resinlayer on the image-forming side of the resin-coated paper typephotographic support was 1.78-0.025% by weight in terms of barium oxidebased on the titanium dioxide, the titanium dioxide pigment was preparedthrough an acid washing step and particle diameter of the titaniumdioxide pigment was 0.114-0.138 μm. On the other hand, even if thetitanium dioxide pigment was prepared through the acid-washing step, dielip stain and microgit both occurred much if analytical value of theclinker was 2.91% by weight in terms of barium oxide and particlediameter-of the titanium dioxide pigment was 0.101 μm. Similarly, whenthe amount of barium oxide was 0.0044% by weight and particle diameterof the titanium dioxide pigment was 0.167 μm, die lip stain andmicrogrit were both less, but sharpness of a printed image was somewhatinferior.

On the other hand, even if amount of barium oxide based on the titaniumdioxide and particle diameter of the titanium dioxide pigment were bothwithin the ranges of the present invention, die lip stain and microgritboth occurred much to cause practical problem in use, when the titaniumdioxide pigment was prepared without the acid-washing step.

EXAMPLE 4

A titanium dioxide pigment was prepared in the same manner as in Example1, except that magnesium chloride was used in place of the predeterminedamount of magnesium sulfate and a photographic support was made in thesame manner as in Example 1. Subsequently, die lip stain and microgritwere examined to obtain the similar results to those in Example 1.

As explained in detail hereabove, the titanium dioxide pigment of thepresent invention is suitable for use in a resin layer of a resin-coatedpaper type photographic support and has the merit that die lip stain andmicrogrit occur quite little even when content of the titanium dioxidepigment is increased in order to enhance sharpness of a printed image.

What is claimed is:
 1. A process for producing a photographic supportcomprising a substrate, at least one side of which is coated with athermoplastic resin composition, wherein the process comprises thefollowing steps:(a) adding at least one alkaline earth metal compound totitanium dioxide in an amount of 0.01-2.0% by weight in terms of a metaloxide based on the titanium dioxide before calcination, and subjectingthe titanium dioxide and alkaline earth metal compound to calcination,(b) acid-washing the titanium dioxide at acidic state after thecalcination and before a step of surface treatment with a hydrated metaloxide, (c) drying the titanium dioxide, (d) grinding the titaniumdioxide, whereby a particle size of the titanium dioxide is 0.110-0.150μm shown by number-average diameter obtained by measuring the diameterin a certain direction using an electron microscope, (e) kneading theresulting titanium dioxide pigment with a thermoplastic resin to obtaina resin composition, and (f) melt-extrusion coating the substrate withthe thermoplastic resin composition.
 2. A process according to claim 1,wherein the thermoplastic resin is a polyolefin resin.
 3. A processaccording to claim 1, wherein the thermoplastic resin compositioncontains an antioxidant.
 4. A process according to claim 3, wherein theantioxidant is a hindered phenol type antioxidant.
 5. A process forproducing a photographic support comprising a substrate, at least oneside of which is coated with a thermoplastic resin composition, whereinthe process comprises the following steps:(a) adding at least onealkaline earth metal compound to titanium dioxide in an amount of0.01-2.0% by weight in terms of a metal oxide based on the titaniumdioxide before calcination, subjecting the titanium dioxide and alkalineearth metal compound to calcination, (b) acid-washing the titaniumdioxide at acidic state after the calcination and before a step ofsurface treatment with a hydrated metal oxide, (c) drying the titaniumdioxide, (d) grinding the titanium dioxide using a fluid energy mill,whereby a particle size of the titanium dioxide is 0.110-0.150 μm shownby number-average diameter obtained by measuring the diameter in acertain direction using an electron microscope, (e) kneading theresulting titanium dioxide pigment with a thermoplastic resin to obtaina resin composition, and (f) melt-extrusion coating the substrate withthe thermoplastic resin composition.
 6. A process according to claim 5,wherein the polyolefin resin in a polyethylene resin.